CH₃ CN@open-C₆₀ : An Effective Inner-Space Modification and Isotope Effect Inside a Nano-Sized Flask

Despite several small molecules being encapsulated inside cage-opened fullerene derivatives, such species have not considerably affected the structures and properties of the outer carbon cages. Herein, we achieved an effective inner-space modification for an open-cage C₆₀ derivative by insertion of a neutral CH₃ CN molecule into the cavity. The CH₃ CN@open-C₆₀ thus obtained showed an enhanced polarity, thus affording an easy separation from a mixture containing the empty cage by column chromatography on silica gel, without the preparative HPLC that was needed for previous cases. The less negative reduction potentials with respect to those of empty cage reflect the decreased energy level of the LUMO, which is supported by the DFT calculations. NMR spectroscopy, single-crystal X-ray analysis, and theoretical calculations revealed that both the presence of the encapsulated CH₃ CN and cage deformation caused by the CH₃ CN play an essential role in the change of the electronic properties. Furthermore, the favored binding affinity of deuterated acetonitrile CD₃ CN with internal C₆₀ surface is discussed.